[PATCH] iio: adc: stm32-adc: fix erroneous handling of spurious IRQs

[Ahmad Fatoum]

Hello Jonathan,

On 16.01.21 18:53, Jonathan Cameron wrote:
> On Tue, 12 Jan 2021 16:24:42 +0100
> Ahmad Fatoum <a.fatoum at pengutronix.de> wrote:
> 
>> 1c6c69525b40 ("genirq: Reject bogus threaded irq requests") makes sure
>> that threaded IRQs either
>>   - have IRQF_ONESHOT set
>>   - don't have the default just return IRQ_WAKE_THREAD primary handler
>>
>> This is necessary because level-triggered interrupts need to be masked,
>> either at device or irqchip, to avoid an interrupt storm.
>>
>> For spurious interrupts, the STM32 ADC driver still does this bogus
>> request though:
>>   - It doesn't set IRQF_ONESHOT
>>   - Its primary handler just returns IRQ_WAKE_THREAD if the interrupt
>>     is unexpected, i.e. !(status & enabled_mask)
> 
> This seems 'unusual'.  If this is a spurious interrupt we should be
> returning IRQ_NONE and letting the spurious interrupt protection
> stuff kick in.
> 
> The only reason I can see that it does this is print an error message.
> I'm not sure why we need to go into the thread to do that given
> it's not supposed to happen. If we need that message at all, I'd
> suggest doing it in the interrupt handler then return IRQ_NONE;

As described, I run into the spurious IRQ case, so I think the message is
still useful (until that's properly fixed), but yes, it should've returned
IRQ_NONE in that case.

With these changes, IRQF_ONESHOT shouldn't be necessary, but in practice
the driver doesn't function correctly with the primary IRQ handler threaded.

Olivier, Fabrice: Are you aware of this problem?

Cheers,
Ahmad

> 
>>   - stm32mp151.dtsi describes the ADC interrupt as level-triggered
>>
>> Fix this by setting IRQF_ONESHOT to have the irqchip mask the IRQ
>> until the IRQ thread has finished.
>>
>> IRQF_ONESHOT also has the effect that the primary handler is no longer
>> forced into a thread. This makes the issue with spurious interrupts
>> interrupts disappear when reading the ADC on a threadirqs=1 kernel.
>> This used to result in following kernel error message:
>>
>> 	iio iio:device1: Unexpected IRQ: IER=0x00000000, ISR=0x0000100e
>> or
>> 	iio iio:device1: Unexpected IRQ: IER=0x00000004, ISR=0x0000100a
>>
>> But with this patch applied (or threaded IRQs disabled), this no longer
>> occurs.
>>
>> Cc: Lucas Stach <l.stach at pengutronix.de>
>> Reported-by: Holger Assmann <has at pengutronix.de>
>> Fixes: 695e2f5c289b ("iio: adc: stm32-adc: fix a regression when using dma and irq")
>> Signed-off-by: Ahmad Fatoum <a.fatoum at pengutronix.de>
>> ---
>>  drivers/iio/adc/stm32-adc.c | 2 +-
>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/drivers/iio/adc/stm32-adc.c b/drivers/iio/adc/stm32-adc.c
>> index c067c994dae2..7e0e21c79ac8 100644
>> --- a/drivers/iio/adc/stm32-adc.c
>> +++ b/drivers/iio/adc/stm32-adc.c
>> @@ -1910,7 +1910,7 @@ static int stm32_adc_probe(struct platform_device *pdev)
>>  
>>  	ret = devm_request_threaded_irq(&pdev->dev, adc->irq, stm32_adc_isr,
>>  					stm32_adc_threaded_isr,
>> -					0, pdev->name, indio_dev);
>> +					IRQF_ONESHOT, pdev->name, indio_dev);
>>  	if (ret) {
>>  		dev_err(&pdev->dev, "failed to request IRQ\n");
>>  		return ret;
> 
> 

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